Thermally operated electric switching mechanisms



Dec. 23, 1958 w. A. COBURN 2,366,035

THERMALLY OPERATED ELECTRIC SWITCHING MECHANISMS Filed April 21, 1955 4 Sheets-Sheet 1 Dec. 23, 1958 w, go U N I 2,866,035

THERMAL-LY OPERATED ELECTRIC SWITCHING MECHANISMS Dec. 23, 1958 w, A, COBURN 2,866,035

THERMALLY OPERATED ELECTRIC SWITCHING MECHANISMS Filed April 21, 1955 4 Sheets-Sheet 3 Dec. 23, 1958 THERMALLY OPERATED ELECTRIC SWITCHING MECHANISMS Filed April 21, 1955 4 Sheets-Sheet 4 w. A. COBURN 2,866,035

THERMALLY OPERATED ELECTRIC SWITCHING MECHANISMS Wallace A. Coburn, Brandon, Manitoba, Canada,

to C. T. Electrical Controls Limited, toba, Canada Application April 21, 1955, Serial No. 502,991 Claims priority, application Canada February 17, 1955 Claims. (Cl. 200116) assignor Brandon, Mani- This invention relates to improvements in thermally operated electric switching mechanisms, and in particular to mechanisms embodying a current totalizing bar of the type described in United States Patent 2,600,734 issued June 17, 1952, to W. A. Coburn and also described in W. A. Coburns United States Patent applications Serial No. 494,343, filed March 15, 1955; and No. 494,459 filed March 15, 1955.

Various forms of mechanisms constructed in accordance with the present invention are illustrated by way of example in the accompanying drawings in which:

Figure 1 is a plan View of a first form of switching mechanism with the cover removed;

Figure 2 is an underside plan view of the apparatus seen in Figure 1;

Figure 3 is a central section on the line III-III in Figure 1;

Figure 4 is a central section similar to Figure 3 but showing a second form of mechanism according to the invention;

Figure 5 is a further central section showing a third form of mechanism according to the invention;

Figure 6 is a diagrammatic end view of a portion of the mechanism seen in Figure 5;

Figure 7 is a view similar to Figure 6 illustrating a further modified form of mechanism according to the invention; and

Figure 8 is a circuit diagram illustrating the operational employment of the form of mechanism illustrated in Figures 1 to 3.

The first form of mechanism, i. e. that shown in Figures 1 to 3, is in the form of a circuit breaker 10, the stationary contacts, moving contacts and manually operable closing mechanism of which are similar to those described in said United States Patent application Serial No. 494,343. This circuit breaker consists of a body shell 11 moulded from a' suitable non-conducting synthetic resinous material. As best seen from Figure 2, the underside of the shell 11 is formed with three parallel longitudinally extending cavities 13, 14 and 15, the central cavity 15 being substantially deeper than the outer cavities 13 and 14. On its upper side the shell 11 has two parallel longitudinally extending lateral cavities 16 and 17, with a platform 18 extending therebetween.

The platform 18 has a transverse passage 19 (see Figure 3), this passage interconnecting the cavities 16 and 17 and accommodating a totalizing bar 20 of insulating material extending transversely across the circuit breaker. This bar 20 has bosses 21 at its ends, such bosses 21 projecting downwardly into cavities 16 and 17. Each boss 21 is formed with a rectangular hole through which a bimetallic strip 23 extends, whereby upward movement of the metallic strips 23 may be transferred to the bar 20 through adjusting screws 24 (Figure 1).

One end of each of the bimetallic strips 23 is fastened to fixed terminals 25 (Figure 1) by rivets 26 (Figure 2). In use, wires (not shown) are connected to these terminals 25 by screws 27. The free end of each of the bimetallic strips 23 passes through a boss 21 of the bar 20 and carries a flexible connecting wire (not visible in the views of this embodiment) whereby individual circuits are completed from the terminals 25 through the bimetallic strips 23 to a pair of movable contacts 28 (Figure 1).

These movable contacts 23 are permanently secured to an f insulating carrier bar 33 extending transversely across the circuit breaker. The upper end of each of the contacts 28 carries a raised contact-making surface of suitable material, such as silver, in the usual way.

The carrier bar 33 which carriers the contacts 28 has a centrally positioned aperture through which a brass rod- 35 extends, as best seen from Figure 3. This rod 35 serves to mount the carrier bar,33 in the circuit breaker,

a helical spring 36 being arranged on the rod 35 extending between a surface on the carrier bar 33 and a fixed projection 38 extending upwardly from the platform 18.

The aperture in this carrier bar is elliptical in cross-section so that the spring 36 will at all times bear against the edges of such aperture to urge the lower part of the carrier bar 33 to the right, while permitting a degree of freedom of tilting motion to such bar.

The movable contacts 28 co-operate with fixed contacts 39 (Figure 1) each secured to a terminal 41 by means of a rivet 40 (Figure 2).

The manually operated mechanism of the circuit breaker consists of an operating handle 29 moulded from a suitable non-conducting material in the shape of a flat circular segment. This operating handle 29 is pivotally mounted on a pin 56 extending between the side walls of a frame member 57. The manually operated mechanism also includes a second frame member 67 slidably mounted in relation to the first frame member 57, and a latch mechanism mounted within the frame member 67, the primary element of this latch mechanism being a latch member 70 (Figure 3) having a free end 68 extending downwardly and into register, in the closed position of the circuit breaker (not illustrated) with the upper surface of the central portion of the totalizing bar 20. The latch mechanism also includes a cam 77 having a step 76 normally in register with the end of the latch member 70 remote from the end 68 thereof already referred to.

As above-stated, this manually operated and latching part of the circuit breaker is identical with that described in said United States Patent application Serial No. 494,343 and it is therefore not deemed necessary herein to provide a thorough description of the detailed parts or of the operation of this mechanism. It will be observed that those parts to which reference has been made have been designated by the same reference numerals as employed in such other application. Suffice to say in this specification that the operating handle 29 is biased to the open position of the switch (Figure 3) by means of a coil spring 84, and that when such dolly is rotated anticlockwise it causes the carrier bar 33 to be moved to the left until the contacts 28 mounted thereon are brought into close engagement with the stationary contacts 39. During this closing operation, a wiping action between each pair of contacts is obtained, as already fully described in the last-mentioned co-pending application.

On the occurrence of an overload in either or both of the two circuits controlled by this circuit breaker, one or other or both of the bimetallic strips 23 will be caused to flex and press upwardly on the screws 24 of the bosses 21 of the totalizing bar 20. This has the effect of elevating the centre of such bar 20 to an extent depending upon thernean elevation of the two ends of such bar. The movement of the centre of the bar 20 is thus a function of the total overload current of the two circuits flowing through the circuit breaker. The purpose, func-' ing application, and will therefore not be repeated here.

The form of apparatus now being described differs from the forms of apparatus described in the earlier appli cations referred to, in that a micro-switch 100 is mounted in the underside of cavity of the shell 11 by means of a bracket 101 secured to the platform 13 of the shell 11 by means of a screw 102, this screw 102 also serving to secure the first frame member 57 of the operating mechanism previously referred to. The micro-switch 100 is pivotally mounted on the bracket 101 by means of a pin 103 (Figure 2).

The micro-switch 100 is of conventional construction, consisting of a snapper 104, the free end of which is movable between a pair of stationary contacts 105 and 106. The snapper 104 has a tongue 107 which is stressed in compression by abutment with a fixed step 108, the main arm of the snapper 104 being secured to the casing 109 of the micro-switch 100 by means of a screw 110 which also acts as a terminal. The micro-switch 100 is completed by an actuating rod 111 which projects outwardly from the casing 109 into engagement with the underside of a central part of the totalizing bar 20. At its inner end the rod 111 enters a member 112 of insulating material which serves to transmit force from the rod 111 to the main arm of the snapper 104. Such transmitting member 112 includes an extension 113 which is arranged above afixed part of the stop 108 so that should the rod 111 be forced too far inwardly of the casing 109 it will come up against firm resistance and will thus not inflict damage to the delicate snapper 104.

The apparatus is completed by a supporting arm 114 that extends centrally along the lowest part of the shell 11 below the cavity 15. An inwardly bent end 115 of the arm 114 bears against the undersurface of the easing 109 of the micro-switch 100. The arm 114 is secured to a broad bent arm 116 which includes a pair of outwardly extending ears 117 that form trunnions for the arms 114 and 116 by virtue of their engagement in respective V-shaped notches 118 formed in a downwardly extending pair of walls 119 that define the cavity 15. The arm 116 is drawn upwardly towards the platform 18 to maintain pressure between the ears 117 and the notches 118, by means of a coil spring 120 (Figure 3) secured at one end to the arm 116 by means of a pin 121 and at its other end to the platform 18 by means of a pin 122. The free end 123 of the arm 116 is further acted upon by an adjusting screw 124 that extends downwardly from a tapered hole in the platform 18, to press against such end 123.

The purpose of the mechanism just described is to provide two independent switches operated by the same totalizing bar 20. This totalizing bar, which is in turn controlled by the bimetallic strips 23, can cause tripping of the manually set mechanism by upward movement of its central portion, as described in the last-mentioned copending application. At the same time, such upward movement of the central portion of the bar will serve to allow the rod 111 to move outwardly of the casing 10? under the urging of the spring snapper 104. This movement of the rod 111 will thus allow the snapper 104 to spring over from the fixed contact 106 to the fixed contact 105. The degree of movement of the centre of the totalizing bar 20 that will be necessary to accomplish this object will depend upon the position of the casing 109 of the micro-switch 100 relatively to its actuating rod 111. Such position will be determined by the setting of the adjusting screw 124. If such screw is drawn upwardly the result will be a slight anti-clockwise rotation of the assembly of arms 114 and 116, so that the end 115 of the arm 114 will press upwardly against the underside of the casing 109. A large degree of upward movement of the actuating rod 111 will then be required before the microswitch would snap over from one position to the other. Conversely, if the screw 124 were screwed downwardly from the platform 18, a smaller movement of the centre veniently be also 40 amps.

of the totalizing bar 20 is all that would be necessary to operate the micro-switch 100.

Typical employment for a device such as shown in Figures 1 to 3, is illustrated in Figure 8. This figure shows a portion of a domestic electricity supply system. The entry switch from the utility wires is shown at 125. This switch is of conventional construction, as is also the fuse panel 126 to which it feeds. The fuse panel 126 in turn feeds power to the circuit breaker 10. The electricity supply is assumed to be the commonly employed threewire, single-phase type, e. g. with 230 volts across the outside leads 128 and 129 and with volts between either of these leads and the central lead 130. The typical domestic loads illustrated are a cooking range 131 and a clothes drier 132. Clearly, the cooking range 131 will form the more essential of these two loads. The connections illustrated show that the cooking range 131 is connected between terminals 25 of the mechanism 10, the terminals 41 being connected to the leads 128 and 129. The central lead 130 is also connected to the cooking range 131, such connection being made permanently through a junction panel 133. The bimetallic strips 23 are thus arranged in the two main outer arms of the circuit to the range 131, so that overloads in such range 131 will cause one or both of these bimetallic strips 23 to trip the main contacts of the circuit breaker 10 and thus open the circuits to such range.

The drier 132 represents a less preferred load, which may be temporarily disconnected without undue inconvenience to the consumer, should the total load exceed a maximum amount agreed upon by the customer and the supplying utility as being the maximum demand to be drawn. The drier actually consists of twoindependent loads, a motor 134 and a heating element 135, the latter representing by far the greater demand on the supply system. it is also the least necessary of the three loads. It will be observed that the motor 134 is connected through the junction panel 133 between one terminal 41 connected to the incoming lead 120 and the central terminal of the panel 133 connected to the incoming lead 130. The motor is thus supplied with 115 volts. On the other hand, the heating element 135 is connected between the terminal 41 connected to the lead 129 and the other terminal 41 which is connected to incoming lead 128, such heating element 135 thus being operated on 230 volts. This latter connection of the heating element 135 is, however, connected to the terminal 11 of the circuit breaker 10 through the micro-switch 100. This circuit is such that when the micro-switch 100 opens the heater element is disconnected but the motor will continue to turn and avoid any possibility of the clothes burning.

By this series of connections there is achieved an arrangement in which the less preferred load, namely the heating element 135 is disconnected, not in accordance with its own demand, but in accordance with the demand of the more preferred load, namely the range 131. Taking a numerical example to illustrate this operation, the maximum demand of the range might he say 40 amps. The rating of the circuit breaker 10 could then con- The heating element 135 might draw for example, 25 amps. The setting of the adjusting screw 124 of the circuit breaker 10 should then be such that the micro-switch 100 will open whenever the load drawn by the range 131 exceeds 15 amps. The main contacts of the circuit breaker 10 would be opened by the bimetallic strips 23 when a load of 40 amps, plus an allowable overload of say 25%, was drawn by the range 131. The arrangement thus provides protection against short circuit faults in the range and enables two appliances, namely the range and the drier, never to draw more than the maximum demand of the range from the line, although the combined maximum demands of the two appliances exceeds quite considerably the maximum rating of the supply switch. In the foregoing considera tions, the load of the motor 134. has been ignored, since it will be very slight in comparison with the other loads and since the circuit breaker is not connected to provide any means for protecting against overloads in such motor. The main fuse panel 126 would take care of any such relatively unlikely occurrence.

It will be appreciated that the simplified circuit illustrated in Figure 8 is only intended to exemplify the operation of the circuit breaker 10 and represents only a portion of any normal domestic or industrial load. More flexibility can be introduced into a more complex system operating on the same principle, by providing more than one micro-switch, each such micro-switch being arranged in series with one or other of the less preferred loads. In this way it is possible to grade the preference of such loads. Devices designed to fulfill this requirement will be referred to more fully below.

Consideration will firstly be given, however, to a second form of mechanism in accordance with the invention, illustrated in Figure 4. This mechanism is similar to that illustrated in Figures 1 to 3 except that the manually operated circuit breaker portion and the movable contacts carried thereby are no longer employed. A similar shell 11 is provided and Figure 4 shows a cover 12 for such shell, it being understood that a similar cover would in fact be employed with the machanism shown in Figures 1 to 3. As before a micro-switch 190 is pivotally mounted on a bracket 101 and its position is controlled by an assembly of arms 114 and 116 mounted in the shell 11 in a similar manner to that previously employed. The adjust ng screw for this as embly is however modified and takes the form of a much longer screw 136 which extends upwardly through a tapped hole in the platform 18 of the shell 11 and also through a clearing hole in the upper portion of the cover 12. An indicating disc 137 is secured to the outwardly projecting end of such screw 136. The disc 137 includes a stop arm 138 which co-operates with a rod 139 which is screwed into the platform 18 and thus serves both as a stop for the arm 138 and as means for holding the cover 12 firmly in position. For this latter purpose the rod 139 includes a conical enlargement 140 which seats in a complementary recess 141 in the upper surface of the cover 12. A scale 142 illustrated diagrammatically by a single line in Figure 4 is employed in co-operation with a scribed line on the indicating disc 137, to determine desired settings of the screw 136. A coil spring 143 is arranged around the projecting enzl of the screw 136 between the surface of the cover 12 and the undersurface of the disc 137. This spring 143 serves to hold the parts firmly and to avoid backlash.

The bimetallic strips 23 are shown only in broken lines in Figure 4, being secured to terminals and extending into bosses at the ends of the totalizing bar 29 as before. Instead, however, of being connected by flexible leads to movable contacts, they are connected by flexible leads shown at 29, to the fixed terminals 41.

The operation of the form of mechanism illustrated in Figure 4 will be generally similar to that of the form of mechanism illustrated in Figures 1 to 3 and no special circuit diagram is deemed necessary to demonstrate such operation. As before, the mechanism will provide for operation of the micro-switch 100 in accordance with the current flowing through the bimetallic strips 23. Thus, the less preferred load connected through the microswitch 109 will be disconnected on attainment of a certain predetermined load through bimetallic strips 23. The value of such latter load will be determined by the position of the screw 136, as manually set by the disc 137. This simplified form of mechanism provides no protecttion against overloads in the main circuit fed through'the bimetallic strips 23, it being presumed that such possibility will be taken care of by other apparatus such as a fuse panel.

Figures 5 and 6 illustrate a still further embodiment of the invention. In this construction two micro-switches 100 and 100' are employed, being arranged on opposite sides of the platform 18 of a shell 11, their actuating rods 111 and 111 into engagement respectively with the under and upper surfaces of the centre of the totalizing bar 20 which is controlled by bimetallic strips (not shown) in the same manner as in the foregoing embodiments. An assembly of arms 114 and 116 acts, as before, on the casing of the micro-switch 100, and adjusting screw 124 similar to that employed in the embodiment of Figures 1 to 3 determining the setiing of this assembly. The micro-switch 100 is pivotally mounted on a bracket 101 similar to the bracket 101 and the position of its casing is determined by means of an arm 144 secured at one end to the projection 38 extending upwardly from the platform 18 and hearing at its free end an adjusting screw 145 extending downwardly into engagement with the casing of the micro-switch 106'. The simplified diagram of Figure 6 shows clearly the transverse relationship of the two micro-switches, the bar 26', its bosses 21 and the bimetallic strips 23. In this case, the cover 12 will be imperforate, except for any hole necessary to accommodate a securing screw, it being normal practice to remove the cover 12' to obtain access to the two adjusting screws 124 and 14S. Assuming that the bimetallic strips 23 will be arranged, as before, to elevate the totalizing bar 20, as the current through such strips increases, the micro-switch 100 will require to be arranged to be opened by outward movement of its actuating rod 111, also as before, whereas the microswitch 100' will need to be arranged for operation by inward movement of its actuating rod 111'. This arrangement can easily be achieved by the setting of the adjusting screw 145 and by selection of the fixed contact corresponding to the contact 165 (see Figure 3) as the operative contact. If preferred, the bimetallic strips 23 may be mounted to flex downwardly when heaied, in which case the operation of the micro-switches would be reversed. It will be usual to arrange for one of the micro-switches to be operated on attainment of a relatively low load in the bimetallic strips 23 and for the other micro-switch to be operated on attainment of a somewhat higher load passing through such strips. It is immaterial which micro-switch is employed as the first one to operate. It clearly will be connected to the least preferred load. As in the case of the embodiment described with reference to Figure 4, no provision is made is this form of the mechanism for opening the circuit passing through the bimetallic strips 23. I

A form of illustration similar to Figure 6 has been employed to show a further embodiment of the invention. This appears as Figure 7, in which it will be seen so as to bring that the centre of the totalizing bar 20 serves to control three micro-switches 100, and 108". The arrangement of the micro-switch 100 beneath the centre of the bar 26 is the same as in the previous embodiments and requires no further detailed explanation. The microswitches 100' and Hit)", which are both arranged above the totalizing bar 26 are disposed in side-by-side relationship, their actuating rods 111' and 111 bearing each on one end of a tilting lever 146. The centre of this lever 146 is provided with an arcuate recess which co-operates with a complementary projection 147 extending upwardly at the centre of the totalizing bar 20 thus serving to mount the lever 146 pivotally. It will be observed that the actuating rods 111 and 111" are spaced sidewardly fro-m the projection 147 by different distances, the actuating rod 111 being nearer to the centre ofthe bar 20. The casings of the micro-switches and 100" are rigidly connected together and pivotally mounted on a bracket (not shown) as a common assembly. Similarly an adjusting screw (not shown) bears on such to determine its vertical position.

The preferred method of use of this last form of the,

invention is to arrange the setting of the two adjustingscrews so that the first micro-switch to be operated, i. e.,.

assemblyat the lowest load through the bimetallic strips, will be the micro-switch 1%, this switch being connected to the least preferred load. Assuming that, after operation of the micro-switch lltlti, the centre of the totalizing bar fit will continue to rise, with increasing load through the bimetallic strips 23, the projection 147 on such bar will carry upwardly the tilting lever 1 Each of the microswitches 1% and 1% will exert, through their actuating rods, a downward spring force against the tilting lever 146. The turning moment exerted on the tilting lever 146 by the downward force of the actuating rod lit will be greater than the opposite turning moment produced by the actuating rod ill, by reason of the greater lever arm of the former rod. This will result in a small anti-clockwise pivoting movement of the lever 146. The righthand end of such lever being thus higher than the lefthand end, the micro-switch 1083 will be the next switch 'to be operated as the bar 2% rises. Once this switch has been operated and the extension 113 of its transmitting member 112 has come into contact with the member 1418, assuming this switch to be constructed as in Figure 3, further upward movement of the actuating rod 111 will be positively prevented. Accordingly, continued upward movement of the projection 147 on the bar 20 will result in a clockwise tilting of the lever 1.46 with ultimate operation of the third micro-switch 109". It will be evident that these three micro-switches will be connected to different loads as determined by the degree of preference of such loads, and the sequence of operation of the switches. Again, it is not thought necessary to illustrate a circuit employing such a device, as such a circuit would represent merely multiplication of the circuit illustrated in Figure 8. Alternatively to the use of different lever arms, the sequential operation of the switches may be determined by providing the two switches with springs of different strength.

If it is desired to control a fourth circuit, a second tilting lever similar to the lever 146 can be arranged beneath the totalizing bar 2% to control two microswitches mounted as a common assembly in the same manner as the micro-switches 10%) and 100".

A valuable feature of this method of arranging the micro-switches on opposite sides of the totalizing bar should be appreciated. When two or four switches are used, the forces exerted on such bar by their springs act in opposition and cancel each other out. When three switches are used, the residual force will be equivalent to that'of one switch, assuming switches with identical springs be used. If this aspect be very important the loading could be balanced by using springs of different strength, when the number of switches on each side of the totalizing bar is not the same. Normally such an expedient is unnecessary, since however many switches are controlled by the totalizing bar, the effort needed to move the same is never greater than that required for operation of one micro-switch.

If desired, the arms controlling the positions of the casings of the micro-switches, e. g. the arm 114 or the arm 144, may themselves be in the form of bimetallic strips, in order to provide ambient temperature compensation in the mechanisms. The manner in which such auxiliary strips can be arranged to provide ambient temperature compensation, is fully described in the said lastmcntioned co-pending application.

Throughout the foregoing description reference has been made to the disconnection of the less preferred load or loads. Alternatively, in any of the cases, the microswitch may be connected so as not wholly to disconnect its less preferred load, but instead to connect such load to a reduced voltage. Thus, a load normally connected across the 230 volt leads can be switched to a pair of leads supplying 115 volts, when a three-wire, single-phase Edison type of supply system such as that illustrated, is employed.

I claim:

1. A thermally operated electric switching mechanism comprising a housing, a pair of independent electric circuits extending through said housing, a totalizing bar movable relatively to said housing, a pair of bimetallic elements each arranged to be heated by the current in a respective one of said circuits and each secured at one end to said housing while acting at its other end on a respective end of said totalizing bar, said bimetallic elements being such as to deflect in the same sense as each other on being heated, a switch casing adjustably mounted on said housing, a switch mechanism in said switch casing, and an actuating member movably mounted in said switch casing for operation of said switch mechanism, said actuating member extending outwardly of said switch casing and being operatively coupled with a part of the totalizing bar intermediate its ends.

2. A mechanism as claimed in claim 1, including a pair of fixed contacts, a pair of ganged contacts movable into and out of contact with each of said fixed contacts whereby to make and break said pair of independent electric circuits, and a latch mechanism for tripping the movable contacts, said latch mechanism being arranged for. actuation by movement of a part of said totalizing bar intermediate its ends.

3. A mechanism as claimed in claim 1, including a pair of fixed contacts mounted in side-by-side relationship, a loosely slidably mounted bar carrying a pair of contacts positioned each for co-operation with one of said fixed contacts, closing means for moving said bar to contacts-engaged position, spring means acting on said bar at a point displaced from the line joining the contact carried by said bar, said spring means urging said bar to contacts-disengaged position, said closing means acting on said bar at a point intermediate between the point of said bar acted upon by the spring means and said line joining the contacts carried by the bar.

4. A thermally operated electric switching mechanism comprising a housing, a pair of independent electric circuits extending through said housing, a totalizing bar movable relatively to said housing, a pair of bimetallic elements each arranged to be heated by the current in a respective one of said circuits and each secured at one end to the housing while acting at its other end on a respective end of said totalizing lever, said bimetallic elements being such as to deflect in the same sense as one another on being heated, a first switch including a pair of parts relative movement between which effects actuation of said switch, one of said parts being mounted on said housing on one side of the totalizing bar, and the other of said parts being operatively coupled with a part of the totalizing bar intermediate its ends, a second switch also including a pair of parts relative movement between which effects actuation of said second switch, one of said parts of the second switch being mounted on said housing on the side of the totalizing bar remote from the first switch and the other of said parts of the second switch being operatively coupled with a part of the totalizing bar intermediate its ends.

5. A thermally operated electric switching mechanism comprising a housing, a pair of independent electric circuits extending through said housing, a totalizing bar movable relatively to said housing, a pair of bimetallic elements each arranged to be heated by the current in a respective one of said circuits and each secured at one end to the housing while acting at its other end on a respective end of said totalizing lever, said bimetallic elements being such as to deflect in the same sense as one another on being heated, two switch mechanisms, a common supporting member for said switch mechanisms mounted on said housing, two actuating members movably mounted relatively to said supporting member each for operation of a respective switch mechanism, a transmitting member pivotally coupled to a part of the totalizing bar intermediate the ends of said bar, said actuating 9 members being operatively coupled with said transmitting member one on each side of the point of pivot of said transmitting member.

6. A mechanism as claimed in claim 5, wherein said actuating members engage said transmitting member at different distances from the point of pivot of said member.

7. A mechanism as claimed in claim 5, wherein the couplings effected by said transmitting member between the actuating members and the totalizing bar are such that movement of said bar will effect actuation of said switches consecutively.

8. A thermally operated electric switching mechanism comprising a housing, a pair of independent electric circuits extending through said housing, a totalizing bar movable relatively to said housing, a pair of bimetallic elements each arranged to be heated by the current in a respective one of said circuits and each secured at one end to the housing while acting at its other end on a respective end of said totalizing lever, said bimetallic elements being such as to deflect in the same sense as one another on being heated, two switch mechanisms, a common supporting member for said switch mechanisms mounted on said housing, two actuating members movably mounted relatively to said supporting member each for operation of a respective switch mechanism, a transmitting member pivotally coupled to a part of the totalizing bar intermediate the ends of said bar, said actuating members being operatively coupled with said transmitting member one on each side of the point of pivot of said transmitting member, a third switch mechanism, a supporting member for said third switch mechanism adjustably mounted on said base on the side of the totalizing bar remote from the first two switch mechanisms, and a third actuating member movably mounted relatively to said last-mentioned supporting member for operation of said third switch mechanism, said third actuating member being operatively coupled with a part of the totalizing bar intermediate its ends.

9. A thermally operated electric switching mechanism, comprising a housing, a pair of electric circuits extending through said housing, a pair of fixed contacts, a pair of ganged contacts movable into and out of contact with a respective one of said contacts whereby to make and break said pair of electric circuits, and a latch mechanism for tripping the movable contacts, an elongated totalizing bar movable relatively to said housing, a pair of himetallic elements each arranged to be heated by the current in a respective one of said circuits and each secured at one end to the housing while acting at its other end on a respective end of said totalizing bar, said bimetallic elements being such as to deflect in the same sense as one another on being heated and in a direction transverse to the extent of the totalizing bar, said latch mechanism being arranged for actuation by movement of a part of said totalizing bar intermediate its ends, and a switch including a pair of parts relative movement between which effects actuation of said switch, one of said parts being mounted on said housing and the other of said parts being operatively coupled with a part of the totalizing bar intermediate its ends.

10. A thermally operated electric switching mechanism, comprising a housing, a pair of electric circuits extending through said housing, a pair of fixed contacts mounted in side-by-side relationship, a loosely slidably mounted bar for carrying a pair of contacts positioned each for cooperation with one of said fixed contacts, closing means for moving said bar to contacts-engaged position, spring means acting on said bar at a point displaced from the line joining the contacts carried by said bar, said spring means urging said bar to contacts-disengaged position, said closing means acting on said bar at a point intermediate between the point of said bar acted upon by the spring means and said line joining the contacts carried by the bar, an elongated totalizing bar movable relatively to said housing, a pair of bimetallic elements each arranged to be heated by the current in a respective one of said circuits and each secured at one end to the housing while acting at its other end on a respective end of said totalizing bar, said bimetallic elements being such as to deflect in the same sense as one another on being heated and in a direction transverse to the extent of the totalizing bar, and a switch including a pair of parts relative movement between which effects actuation of said switch, one of said parts being mounted on said housing and the other of said parts being operatively coupled with a part of the totalizing bar intermediate its ends.

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